Beryllium-aluminum-silicon composite



April 15, 1969 R. H. KROCK ET AL 3,438,751

BEBYLLIUM-ALUMINUM-SILICON COMPOSITE Filed March 25, 1967 Sheet of 2WEIGHT PER CENT SILICON 2 0 3 0 40 50 60 70 80 90 0 IO 50 IOO ATOMIC PERCENT SILICON ALUMINUM-SILICON PHASE DIAGRAM IN VE N TORS RICHARD H.KROCK EARL l. LARSEN CLINTFORD R. JONES ATTORNE Y April 15, 1969 R. H.KROCK ET AL 3,438,751

BERYLLIUM-ALUMINUM-SILICON COMPOSITE Filed March 23, 1967 Sheet 2 of 2FJZJ1 5 INVENTORS RICHARD H. KROCK EARL LARSEN BY CLlNTFORD R. JONES ATTORNEY United States Patent fice 3,438,751 BERYLLIUM-ALUMINUM-SILICONCOMPOSI'I'E Richard H. Krock, Peabody, Mass., Earl I. Larsen,

Indanapolis, 1116., and Clntford R. Jones, Arlington, Mass., assignorsto P. R. Mallory & Co. Inc.,

Indianapolis, Ind., a corporation of Delaware Filed Mar. 23, 1967, Ser.No. 625,377

Il1t. Cl. B22f 7/00 U.S. Cl. 29-182.1 4 Clams ABSTRACT OF 'lI-IEDISCLOSURE A two-phase composite material whose microstructure consistsof pure beryllium dispersed in an aluminumsilicon-beryllium heattreatable matrix phase was prepared by liquid phase sintering pressedpowder mixtures of beryllium, aluminum and silicon.

types of sintering techniques in that the sintering of the compact iscarried out in the presence of a liquid phase. Liquid phase sinteringencompasses raising the temperature of the compressed powder metalconstituents of beryllium, aluminum and silicon to a temperature whereina predetermined amount of the liquid phase appears. In the liquid phase,one of the metal constituents, the solid, is progressively dissolved inthe other metal constituent or constituents, the liquid. However, thequantities of these constituents are such that, at equilibrium, somesolid phase always exists. It is thought that the liquid wets the solidso as to bring about favorable surface energies existing between theliquid and the solid thereby permitting solution into the liquid phase.

However, heretofore, when beryllium-atluminum-silicon composites werefabricated in accordance with known liquid phase sintering techniques,it was found that the solid beryllium expelled the liquidaluminum-siliconberyllium alloy from the compact during liquid phasesintering. It is thought that the unfavorable surface energy equilibriumcausing expulsion of the liquid aluminum-silicon-beryllium alloy is dueto a tough, tenacious film of beryllium oxide which is present on eachparticle of beryllium.

The present invention prevents the expulsion of the liquidaluminum-silicon-beryllium alloy from the specimen by using an agency tointervene in the sintering stage. The agency either breaks down theoxide film on the beryllium or segregates to the metal oxide interfaceand lowers the surface energy of the liquid metal with respect to theberyllium oxide film so that the liquid metal progressively dissolvesthe solid metal.

The agency can be called a fluxing agent or flux, however, the agent hasother characteristics which assist in wetting beryllium so as tosurround the beryllium with a ductile envelope phase ofaluminum-silicomberyllium alloy matrix metal thereby avoiding theexpulsion of the liquid from the specimen.

Beryllium has several desirable physical features which malte itattractive for a variety of commercial applications such as lightweightgears,"lightweight fasteners, airplane parts or the like. However,beryllium has one major drawback which has seriously limited itscommercial acceptance, that is, beryllium is inherently brittle at roomtemperature.

The lack of ductility of beryllium is attributed to the 3,438,751Patented Apr. 15, 1969 crystal structure of beryllium which is hexagonalclose packed. During deformation, the basal planes of the hexagonalclose packed structure, being the easiest to slip, are aligned along theworking direction. Since slip is crystallographically difficultperpendicular to the basal plane, the ductility of berylliumperpendicular to the primary fabrication direction is practicallynonexistent.

Several possible solutions have been advanced in an attempt to makeberyllium metal suflicently ductile so as to permit a Widespreadcommercial acceptance of beryllium. Cross-rolling and cross-forging havebeen suggested as fabrication methods which might enhance the ductilityof beryllium. These fabrication techniques reduced the number of basalplanes along the direction of rolling and resulted in improvedductility. However, the degree of improvement was far from satisfactory.The fact remained that beryllium must be classified as brittle at roomtemperature even utilizing the aforementioned method when ductilityperpendicular to the fabrication temperature is considered. In addition,the above-mentioned technique would not be feasible where thefabrication is, by nature, solely along one axis such as swaging,drawing and extrusion.

In recent years, attention has been directed to the fabrication ofberyllium alloys not having the inherent brittleness of beryllium itselfbut possessing various outstandng properties of the metal such as, forexample, low density combined with high strength. It is thought thatU.S. Patent 3,082,521 fabricated the first ductile beryllium alloy byrapidly cooling the part from a temperature at which it was liquid.However, the beryllium content of the alloy was not in excess of 86.3atomic percent which is approximately 33 weight percent of the alloy.Although the beryllium alloy was ductile, the density of the alloy wasin excess of that of alurninum and about equal to that of titanium.

It has also been suggested that beryllium alloys might be fabricated bypressing and sintering a mix of metal powders. However, such a methodresults in expulsion of the matrix metal or metals from the berylliumspecimen and the eventual freezing of the matrix metal or metals intoglobs on the surface of the solid specimen. As stated hereinbefore, itis thought that the expulsion of the matrix metal or metals is due tothe surface energies of the solid beryllium and the various liquidsformed. The unfavorable surface energy equilibrium is believed to be dueto a tough, tenacious film of beryllium oxide which is present on eachparticle of beryllium.

A means and method have been discovered for preparing a composite ofberyllium, aluminum and silicon containing about 50 to percent, byweight, of beryllium, about 13.05 to about 50.0 percent, by weight,aluminum and a trace to about 6.6 percent, by weight, silicon, therebyproducing a composite having a density about the same as or less thanthat of aluminum, having high strength, and having good ductility. Theductility s due to the resulting microstructure of the composite. Bysurrounding the beryllium particles with a ductile envelope phase, acomposite is formed where, under load, the beryllium is so constrainedby the ductile phase that it and the ductile phase deform continuously.

The 85 percent, by weight, beryllium composite showed a considerableamount of particle contiguity and would represent, it is thought, anupper lirnit on the percent by weight of beryllium contained by thecomposite. A decrease in beryllium content below 50 percent would raise,it is thought, the density value of the composite to a value of littleinterest.

Alkali and alkaline earth halogenide agents such as lithiumfluoride-h'thium chloride or the like in a determined ratio are utilizedto segregate to the solid interface of the beryllium particle and eitherbreak down the film on the particle of beryllium and/or alter theliquid-solid surface energy in the system.

Therefore, it is an object of the present invention to provide a ductilecomposite of beryllium-aluminum-silicon in which beryllium is thepredominate ingredient.

Another object of the present invention is to provide an agent topromote liquid phase sintering of a berylliumaluminum-silicon mixture.

Yet another object of the present invention is to provide a composite ofberyllium-aluminum-silicon wherein the silicon grains are modified bythe addition of small amounts of metallic sodium so as to precipitateout as rounded globules rather than as angular plates thereby producinga more ductile composite.

A further object of the present invention is to provide an agent whicheliminates the expulsion of an alloy of aluminum-silicon-beryllium froma beryllium specimen.

Yet still another object of the present invention is to provide acomposite of beryllium-aluminum-silicon wherein the composite may besintered to substantially theoretical density.

Still another object of the present invention is to provide a ductileberyllium-aluminum-silicon composite baving a. low density and highstrength.

Yet still another object of the present invention is to provide a meansand method of producing a ductile composite ofberyllium-aluminum-silicon wherein the microstructure consists ofberyllium particles surrounded by a ductile envelope phase of analuminum-silicon-beryllium alloy matrix metal.

Another object of the present invention is to provide a ductileberyllium-aluminum-silicon composite having a matrix phase that is heattreatable.

Yet another object of the present invention is to provide a ductilecomposite of beryllium-aluminum-silicon containing about 50 to 85percent, by weight, beryllium, about 13.05 to 50.0 percent, by weight,aluminum and a trace to about 6.6 percent, by weight, silicon.

Stil] another object of the present invention is to provide alkali andalkaline earth halogenide agents used in the fabrication of aberyllium-alominum-silicon composite.

Another object of the present invention is to provide a ductilecomposite of beryllium-aluminum-silicon containing about 50 to 85percent, by weight, beryllium, and an alloy of aluminum-siliconcontaining about 87.0 to about 100.0 percent, by weight, aluminum, theremainder silicon.

A further object of the present invention is to provide a lithiumfluoride-lithium chloride agent for promoting liquid phase sintering ina beryllium, aluminum and silicon mix.

Yet still another object of the present invention is to provide alithium fluoride-lithium chloride agent wherein the constituents areused in a predetermined ratio.

Yet another object of the present invention is to provide a means andmethod whereby a ductile berylliumaluminum-silicon composite may besuccessfully fabricated in both a practical and economical manner.

The present invention, in another of its aspects, relates to novelfeatures of the instrumentalities of the invention described herein forteaching the principal object of the invention and to the novelprinciples employed in the instrumentalities whether or not thesefeatures and principles may be used in the said object and/or in thesaid field.

With the aforementioned objects enumerated, other objects Will beapparent to those persons possessing ordinary skill in the art. Otherobjects will appear in the following description and appended claims.The invention resides in the novel combination of elements and in themeans and method of achieving the combination as hereinafter describedand more particularly as defined in the appended claims.

In the drawings:

FIGURE 1 is a phase diagram for binary alloys of aluminum-silicon.

FIGURE 2 is an enlarged beryllium base specimen illustrating analuminum-silicon-beryllium matrix metal expelled from the specimen bythe forces of surface energy f sglid beryllium and thealuminum-silicon-beryllium 1qui FIGURE 3 is a photomicrograph of about70 percent, by weight, beryllium, about 26.5 percent, by weight,alumlnum, remainder silicon composite illustrating beryllium particlessurrounded by an envelope phase of an aluminum-silicon-beryllium alloy.

FIGURE 4 is a photomicrograph of about 70 percent, by weight, beryllium,about 26.5 percent, by weight, aluminum, remainder silicon compositeillustrating a modified alloy matrix surrounding the berylliumparticles.

FIGURE 5 is a photomicrograph of about 70 percent, by weight, beryllium,about 26.5 percent, by weight, alummum, remainder silicon compositeillustrating a modified alloy matrix surrounding the beryllium particlesyvl1erein the alloy matrix has been subjected to solution- 1z1ng andhardening treatments.

Generally speaking, the means and method of the present invention relateto a ductile beryllium-aluminumsilicon composite fabricated by liquidphase sintering to substantially theoretical density. The compositecontains about 5085 percent, by weight, of beryllium, about 13.05 to50.0 percent, by weight, aluminum, and a trace to about 6.6 percent, byweight, silicon.

-The method of producing the berryllium-aluminumsilicon composite byliquid phase sintering comprises the steps of mixing predeterminedportions of powder beryll1um and powder alloy of aluminum-silicon oraluminum powder and silicon powder With a predetermined portion of anagent selected from the group consisting of alkali and alkaline earthhalogenides. The portions are pressed 111 a die to form a green compact.The compact is then heated to the sintering temperature of beryllium. Atthis temperature the agent provides a favorable surface energy equrlibrium between the beryllium and the aluminums1licon alloy so thatthe alloy progressively dissolves the beryllium at the sinteringtemperature so as to form an aluminum-silicon-beryllium alloy matrix.Thereafter, the beryllium-aluminum-silicon composite may be heat treatedto further enhance the physical properties of the matrix pl 1ase of thecomposite. Small amount sof metallic sod1um may be added to the powderconstituents prior to compactxng so as to provide, upon sintering, amodified alloy matrix wherein the silicon tends to precipitate out asrounded globules rather than as angular plates as in the unmodifiedalloy matrix. The appearance of rounded globules of silicon instead ofangular plates of silicon increases the ductility of the alloy matrix ofthe composite.

More particularly, the method of the present invention comprises mixingpowder beryllium of about 50-85 percent, by weight, With a powder alloyof aluminum-silicon or the elemental powders of aluminum and silicon. Anagent of lithium fluoride-lithium chloride in about 0.5 to 2.0 percent,by weight, of the total metal additions is mixed With the beryllium orWith the beryllium and the alloy powder or elemental powder. Theconstituents of the agent are in about a one to one ratio by Weight. Theberyllium, the alloy powder or elemental powder, and the agent arepressed so as to form a green compact. The green compact is heated in anon-oxidizing atmosphere such as argon at a temperature of about 900centigrade to about 1150 centigrade. At the aforementioned temperature,the agent provides a favorable surface energy equilibrium between theberyllium and the alloy so that the aluminum-silicon alloy progressivelydissolves the beryllium. The microstructure of the resultant compositeconsists of beryllium particles surrounded by a ductile envelope phaseof an aluminum-silicon-beryllium alloy matrix metal. The alloy issintered to substantially its theoretical density. The allow may bespecially heattreated to enhance the physical properties of the matrixphase.

In carrying out the present invention, a beryllium base compact isfabricated by any suitable means such as powder metallurgy techniques. Asuggested method utilizing this technique is to mix beryllium powderwith an agent of equal parts of lithium fluoride-lithium chloride. Themilling is carried out for about 1 hour using ceramic balls. Thereafter,a powder alloy of aluminum-silicon or the elemental powders are ballmill mixed with the beryllium and the agent for an additional hour. T heblended and mixed powders are compacted to form a green compact byaccepted metallurgical methods such as by compacting Within the confinesof a die in a hydraulic or an automatic press or by placing the powdersin a rubber or a plastic mold and compacting in a hydrostatic press. Thegreen compact is sintered in a non-oxidizing atmosphere such as argon orthe like at a temperature of about 900 centigrade to about 115 0centigrade. It is seen that the range of the sintering temperatures isbelow the 1277" centigrade melting point temperature of the berylliumand is above the 577 centigrade melting point temperature Of thealuminum-silicon alloy. The aluminum-silicon a1- loy Will dissolvesmaller beryllium particles and Will dissolve the surfaces of the largerberyllium powder particles so as to surround the remaning berylliumparticles with a ductle envelope phase of aluminum-silicon-berylliumalloy during sintering of the compact. The resultant composite ofberylliurn-aluminum-silicon had a density of about 99.2 percent oftheoretical density.

Composites containing about 50 to 85 percent, by weight, of beryllium,and the remainder an alloy of aluminum-silicon were successfullyfabricated. The agent prevented the expulsion of the liqudaluminum-silicon-beryllium alloy from the compact by the forces ofsurface energy, that is, prevented the formafion of vefy fine roundeddroplets of the aluminum-silicon-beryllium alloy on the surface of theberyllium specimen. FIGURE 2 shows a beryllium speciment 20 having onthe surface thereof an expelled alloy 21 of aluminum-silicon-beryllium.Specimens from which the aluminum-silicon-beryllium alloy has beenexpelled have gross porosity and as a result are weak, brittle, and oflittle commercal value.

The composition of the agent utilized is about 50 parts, by weight, oflithium fluoride to about 50 parts by weight, of lithium chloride. Theagent provides an action, such that upon heating or sintering of thepressed powder mix to the temperature at which the liqud phase forms,expulsion of the melt from the specimen is eliminated. Furthermore, itwas found that solution of the beryllium into the alloy was enhanced asevidenced by the rounded particles by beryllium in the micro-structure.

It was found that the amount by weight of lithium fluoride-lithiumchloride agent should exceed 0.5 percent, by weight, of the total of allmetal additions. It would appear that the optimum range of the agent isfrorri about 0.5 percent to about 2.0 percent, by weight, of the totalof all metal additions. It is believed that the quantity of lithiumfluoride-lithium chloride agent required is related to the amountnecessary to cover the total beryllium surface area. Hence, the minimumamount of agent needed would be a fnnction of the surface area of theberyllium powder. The utilization of lithium fluoride-lithium chlorideagent in other than equal parts is possible. It is thought, however,that an equal parts mixture achieves optimum results.

It was found during sintering that substantially 100 percent of thefluxing agent was lost. This resultant would seem to indicate that thefluoride and chloride portion of the fluxing agent volatilzed and thelithium portion of the fluxing agent slagged and/or volatilized duringthe liqud phase sintering operation.

By using the methods of the present invention and the lithiumfluoride-lithium chloride agent, compacts were fabricated containing upto percent, by weight, of beryllium, the remainder an alloy ofaluminum-silicon without the use of pressure during sintering. Thecomposite was sintered to about 93.5 percent of its theoretical densityby a single sinter and achieved about 98 percent of theoretical densityby a repress and an intermediate reliquid phase sinter for about 1 hour.Using powder beryllium having a particle size of 20 microns or finer andusing ceramic balls to blend the powder metals and the agent resulted ina composite having a density of about 99.92 percent of theoreticaldensity by a single sinter. The good strength and low densitycharacteristics of the beryllium were ret-ained and the resultingberyllium-aluminum-silicon composite possessed good ductility.

Thus, by substantially surrounding the beryllium partcles with a ductleenvelope phase of an aluminum-siliconberyllium alloy matrix metal, theberyllium and the matrix metal deform continuously under load.

An aluminum-silicon phase diagram is illustrated in FIGURE 1.

Silicon is an effective material for strengthenng aluminum. A11 thealuminum silicon alloys show some ductility since alpha aluminum is thecontinuous phase in the eutectic composition. However, since in normalalloys the eutectiferous silicon crystallites tend to be angular plateswhose sharp edges act as internal notches in the structure therebyserving as nucleation sites for fracture so as to reduce the ductilityof the alloy. FIGURE 3 shows the angular plates of silicon 12 formed inthe matrix 11 surrounding the beryllium particles 10. Modification ofthe alloy system can be achieved by small additions of metallic sodiumwhich substantially suppresses the nucleation of the silicon crystals,lowers the eutectic temperature from 577 C. to 550-560 C. and increasesthe silicon in the eutectic composition from about 11.7 percent, byweight, to about 12- 13 percent, by weight. FIGURE 4 illustrates therounded globules of silicon 12 forrned in the matrx 11 surrounding theberyllium particles 10.

As seen above, two important eir'ects are noted as a result of theaddition of metallic sodium into aluminumsilicon melts, that is theproeutectic and eutectic silicon tends to precipitate out in the form ofrounded globules rather than as angular plates and the eutectic pointshifts from about 11.7 percent, by weight, silicon to about 13 percent,by weight, silicon.

The phase diagram of aluminum-silicon shown in FIG- URE 1 illustratesthat the eutectic composition of the normal alloy is about 11.7 percent,by weight, silicon meaning that alloys of less than 11.7 percent siliconWill precipitate out proeutectic aluminum and alloys with greater than11.7 percent silicon Will precipitate out proeutectic silicon. Thesodium modification treatment shifts the eutectic point to about 13percent, by weight, silicon, thus in the modified alloy, a 12 percent,by weight, silicon alloy will precipitate out proeutectic aluminumrather than proeutectic silicon as the phase diagram of the normal alloywould indicate.

Assuming a compact of about 50-85 percent, by weight, beryllium, theremainder an aluminum-silicon alloy with silicon less than 1.65 percent,by weight, to aluminum, with no addition of metallic sodium, heating ofthe compact is carried out at about 900-1150" C. followed by cooling toroom temperature. The composite consists of beryllium particlesdispersed in an aluminum-silicon alloy matrix. Heating the composite toabout 570 C. will dissolve all the silicon into the aluminum. Quenchingthe composite from the elevated temperature preservcs structure obtainedat the elevated temperature, hence, the aluminum matrix issupersaturated with respect to silicon srnce aluminum can dissolve about1.65 percent, by weight, s1licon -at 570 C. and can dissolve virtuallyno silicon at room temperature. The supersaturated matrix can beprecrprtation hardened by a tempering treatment at 300-400 C. for about1-2 hours which will precipitate the silicon 7 that is supersaturated inthe aluminum lattice as a second phase in the aluminum matrix. FIGUREillustrates the composite after it has been precipitation hardened.Beryllium particles 10 are surrounded by a matrix 11 includingprecipitated silicon particles 12.

In the situation of a composite having 50-85 percent, by weight,beryllium, the remainder an unmodified alloy of aluminum-silicon withsilicon less than 11.7 percent, by weight, the alloy is hypoeutectic andupon cooling from the sintering temperature, proeutectic aluminumcrystals are precipitated. Since the alloy is unmodified, the eutecticsilicon appears as angular plates whose sharp edges act as internalnotches in the structure thereby reducing the ductility of thestructure. When the composites are subjected to solutionizing thehardening treatments, as described above, the aluminum rich part of theeutectic reacts as described hereinabove. In addition, the solutionizingtreatment slightly coarsens and rounds the eutectic silicon.

In composites wherein the aluminum-silicon matrix is modified by theaddition of about 0.25 percent, by weight, metallc sodium, the eutecticis driven to about 13 percent, by weight, silicon. Thus, in compositeswherein the percent by weight of silicon is greater than 1.65 percentand less than 13 percent, ali proeutectic precipitate on cooling fromthe sintering temperature is still aluminum crystals, and as discussedabove, the eutectic silicon grains are now rounded rather than angularplates. Solutionizing and tempering has the effect of hardening thealuminum rich part of the eutectic composition as discussed above and inaddition, coarsens the size of the rounded eutectic silicon richcrystals.

Comp0sites having a silicon content in excess of 11.7 percent, byweight, relative to aluminum in the normal or unmodified alloy andsilicon contents in excess of 13 percent, by weight, in modified alloys,the proeutectic phase is silicon rich crystals. The modified alloyswould consist of beryllium particles in an aluminum-silicon eutecticmatrix with some proeutectic silicon crystals present. In modifiedalloys, the shape of both the proeutectic and eutectic silicon crystalswould be rounded, in unmodified alloys, the shape of the proeutectic andeutectic crystals of silicon would be angular plates. Otherwise,treatments and microstructure changes are as described above.

As with the fluxing agent, the sodium addition tends to slag and/orvolatilize from the composite during liquid phase sintering.

Example 1 shows the expulsion of the liquid from a beryllium specimenand Examples 2-14 are illustrative of the preparation ofberyllium-aluminum-silicon composites by liquid phase sintering.

Example 1 Expulsion of the liquid aluminum-silicon-beryllium alloy fromthe solid beryllium specimen during liquid phase sintering When theagent of lithium fluoride-lithium chloride is not used in thepreparation of a beryllium-aluminum-silicon composite, and wherein thealloy matrix is unm0dified.

A mixture of about 70 percent, by weight, of beryllium having a particlesize of 200 mesh or finer was ball mill mixed with about 30 percent, byweight, of an unmodified alloy of aluminum-silicon or the elemenalpowder of suitable particle size. The alloy contained about 88.3percent, by weight, aluminum and about 11.7 percent, by weight, silicon.The milled mixture was pressed by any suitable means such as by anautomatic press at a suitable pressure to provide a green compact sturdyenough to be handled. It was found that pressures of from about 15,000to 20,000 pounds per square inch resulted in a green compact having adensity from about 50 to 60 percent of theoretical density andsufiicicntly strong to be handled. Sintering of the compact was carriedout in an argon atmosphere at about 1100 centigrade for about 1 hour.This technique, due to the surface energies of the solid beryllium andthe liquid formed,

resulted in the expulsion of the liquid from the specimen and itseventual freezing into rounded globs on the surface of the specimen asshown in FIGURE 2.

Example 2 A composite of about 70 percent, by weight, beryllium, about26.5 percent, by weight, aluminum, and the remainder silicon, thecomposite having an unmodified alloy matrix.

A mixture of about 70 percent, by weight, beryllium powder having aparticle size of 200 mesh or finer was ball mill mxed with about 30percent, by weight, of an alloy of aluminum-silicon powder of suitableparticle size. The alloy contained about 88.3 percent, by weight,aluminum and about 11.7 percent, by weight, silicon. Also ball millmixed with the beryllium and alloy powders was about 1.0 percent, byweight, of the total metal additions equal parts of an agent of lithiumfluor delithium chloride. Mixtures of the beryllium and alloy powderswere also prepared with the agent having 0.5 and 2.0 percent, by weight,of the total metal additions. The milled mixture was pressed by anysuitable means such as by an automatic press at a suitable pressure toprovide a green compact sturdy enough to be handled. It was found thatpressures of from about 15,000 to 20,000 pounds per square inch resultedin a green compact baving a density of from 50 to 60 percent oftheoretical density and sufiiciently strong to be handled. The compactwas sintered and repressed. Resintering of the compact was carried outin an argon atmosphere at about 1100 centigrade for about 1 hour raisedthe density of the composite from about 93.5 percent to about 98 percentof theoretical density. The composite is heat-treated at about 570centigrade for about 1 hour SO as to completely dissolve all the silic0ninto the aluminnm. The composite is then rapidly quenched so that thestructure at the heat-treating temperature is preserved and the aluminumis super-saturated with silicon. The supersaturated matrix can beprecipitation hardened by an ageing treatment at 300-400 C. for 1-2hours which will precipitate the silic0n that was supersaturated in thealuminum lattice as a second phase in the matrix.

Example 3 A composite of about 70 percent, by weight, beryllium, 26.5percent, by weight, aluminum, and the remainder silicon, the compositehaving a modified alloy matrxx.

A mixture of beryllium powder having a particle size of 20 micron orfiner was ball mill mixed with about 2.0 percent, by weight, of thetotal metal additions egual parts of an agent of lithiumfluoride-lithium chloridc. The milling was carried out with ceramicballs for abou: 1 hour. Thereafter, an alloy powder of 88.3 percent, byweight, aluminum, 11.7 percent, by weight, silicon., and .25 percent byWeight of the alloy additions of metallic sodium were ball mill mixedwith the beryllium and the agent for about 1 hour. Ceramic balls wereused to mix the powders. The beryllium constituted about 70 percent, byweight of the blended powders and the alloy powder constituted about 30percent of the blended powders. Mix. tures of the beryllium and alloypowders were also prepared with the agent having 0.5 and 1.0 percent, byweight, of the total metal additions. The milled mixture was pressed byany suitable means such as by an automatic press at a suitable pressureto provide a green compact sturdy enough to be handled. It was foundthat pressures of from 15,000 to 20,000 pounds per square inch resultedin a green compact having a density cf from about 50 to 60 percent oftheoretical density and sufliciently strong to be handled. The compactwas sintered and repressed. Resintering of the compact was carried outin an argon atmosphere at about 1150 centigrade for about 1 hour.Another composite was prepared using the above procedure but sinteredfor about '/2 hour. It was found that the composite sintered for 1 hourhad a density of about 99.92 percent of theoretical density and thecomposite sintered for about /2 hour had a. density of about 99.85percent of theoretical density. Bach composite was heat-treated at about570 ccntigrade for about 1 hour so as to dissolve the silicon into thealuminum. Several of the modified composites were precipitation hardenedby an ageing treatment at about 400 centigrade for about 1 hour so thatthe silicon that was supersaturated in the aluminum lattice precipitatesas a second phase in the matrix. Other composites were precipitationhardened using a time-temperature treatment of 2 hours at 300 C.

Example 4 A composite of about 70 percent, by Weiglzt, beryllium, about26.5 percent, by weight, aluminurn, and the remainder silicon, thecomposite having a modified alloy matrix.

The procedure of Example 3 was followed using about 70 percent, byweight, beryllium about 26.5 percent, by weight, aluminum powder, andthe remainder silicon powder. Individual composites were prepared using0.5, 1.0 and 2.0 percent, by weight, of the total metal additions of theagent lithium fluoride-lithium chloride at temperatures of 1000centigrade for /2 hour and 1 hour using the aforementioned procedure.

Example 5 A composite of about 70 percent, by weight, beryllium, about26.5 percent, by weight, aluminum, and the remainder silicon, thecomposite having a modified alloy matrix.

The procedure of Example 3 was followed using about 70 percent, byweight, beryllium powder, mixed With about 30 percent, by weight, of analloy powder of aluminum-silicon. The alloy contains 88.3 percent, byweight. aluminum and 11.7 percent, by Weight, silicon. Individualcomposites were prepared using 0.5, 1.0 and 2.0 percent, by weight ofthe total metal additions of the agent lithium fluoride-lithium chlorideat temperatures of about 900 centigrade for /2 hour and 1 hour using theaforementioned procedure.

Example 6 A composite of about 50 percent, by weight, beryllium, about49.18 percent, by weight, aluminum, and the remainder silicon, thecomposite having a modified alloy matrix.

The procedure of Example 3 was followed using 50 percent, by weight,beryllium powder, mixed With about 50 percent, by weight, of an alloypowder of aluminumsilicon. The alloy contained about 98.35 percent, byweight, aluminum and about 1.65 percent, by Weight, silicon. Individualcomposites were prepared using 0.5, 1.0 and 2.0 percent by weigbt of thetotal metal additions of the agent lithium fiuoride-lithium chloride attem: peratures of about 900, 1000, 1100 and 1150 centigrade for /2h0111and for 1 hour using the aforementioned procedure.

Example 7 A composite of about 50 percent, by weight, beryllium, about43.5 percent, by weight, aluminum, and the remainder silicon, thecomposite having a modified alloy matrix.

The procedure ofExample 3 was followed using 50 percent, by weight,beryllium powder, mixed With about 50 percent, by weight, of an alloypowder of aluminumsilicon. The alloy contained about 87.0 percent, byweight, aluminum and about 13.0 percent, by weight, silicon. Individualcomposites were prepared using 0.5, 1.0 and 2.0 percent by weight of thetotal metal additions of the agent lithium fluoride-litbium chloride attemperatures of about 900, 1000, 1100" and 1150 centigrade using theaforementioned procedure.

10 Example 8 A composite of about 60 percent, by weight, beryllium,about 39.34 percent, by weight, aluminum, and the remainder silicon, thecomposite having a modified alloy matrix.

The procedure of Example 3 was followed using about 60 percent, byweight, beryllium powder, mixed With about 40 percent, by weight, of analloy powder of aluminum-silic'on. The alloy contained about 98.35percent, by Weight, aluminum and about 1.65 percent, by weight, silicon.Individual composites were prepared using 0.5, 1.0 and 2.0 percent byweight of the total metal additions of the agent lithiumfluoride-lithium chloride at temperatures of about 900, 1000, 1100 and1150 centigrade for /2 hour and for 1 hour using the aforementionedprocedure.

Example 9 A composite of about 60 percent, by Weight, beryllium, about34.8 percent, by weight, aluminum, and the remainder silicon, thecomposite having a modified alloy matrix.

The procedure of Example 3 was followed using about 60 percent, byweight, beryllium powder, mixed With about 40 percent, by weigbt, of analloy powder of aluminum-silicon. The alloy contained about 87 percent,by Weight, aluminum and about 13 percent, by weight, silicon. Individualcomposites were prepared using 0.5, 1.0 and 2.0 percent by weight of thetotal metal additions of the agent lithium fluoride-lithium chloride attemperatures of about 900, 1000, 1100 and 1150 centigrade using theaforementioned procedure.

Example 10 A composite of about 75 percent, by weight, beryllium, about21.75 percent, by weight, aluminum, and the remainder silicon, thecomposite having a modified alloy matrix.

The procedure of Example 3 was followed using 75 percent, by weight,beryllium powder, mixed With about 25 percent, by weight, of an alloypowder of aluminumsilicon. The alloy contained about 87 percent, byWeight, aluminum and about 13 percent by weight, silicon. Individualcomposites were prepared using 0.5, 1.0 and 2.0 percent by weight of thetotal metal additions of the agent lithium fluoride-lithium chloride attemperatures of about 900, 1000", 1100 and 1150 centigrade for V2 hourand for 1 hour using the aforementioned procedure.

Example 11 A composite of about 75 percent, by weight, beryllium, about24.59 percent, by Weight, aluminum, and the remainder silicon, thecomposite having a modified alloy matrix.

The procedure of Example 3 was followed using about 75 percent, byweight, beryllium powder, mixed With about 25 percent, by weight, of analloy powder of aluminum-silicon. The alloy contained about 98.35percent, by weight, aluminum and about 1.65 percent, by weight, silicon.Individual composites were prepared using 0.5, 1.0 and 2.0 percent byWeight of the total metal additions of the agent lithiumfluoride-lithium chloride at temperatures of about 900, 1000, 1100 and1150 centigrade using the aforementioned procedure.

Example 12 A composite of about percent, by weight, beryllium, about13.05 percent, by weight, aluminum, and the remainder silicon, the alloyhaving a modified alloy matrix.

The procedure of Example 3 was followed using about 85 percent, byweight, beryllium powder, mixed with about 15 percent, by weight, of analloy powder of aluminum-silicon. The alloy contained about 87 percent,by Weight, aluminum and about 13 percent, by weight, silicon. Individualcomposites were prepared using 0.5, 1.0

11 and 2.0 percent, by weight of the total metal additions of the agentlithium fluoride-lithiurn chloride at temperatures of about 900, 1000,1100 and 1150 centigrade for /2 hour and 1 hour using the aforementionedprocedure.

Example 13 A composite of about 85 percent, by weight, beryllium, about14.75 percent, by weight, aluminum, and the remainder silicon, the alloyhaving a modified alloy matrix.

The procedure of Example 2 was followed using about 85 percent, byweight, beryllium powder, mixed with about 15 percent, by weight, of analloy powder of aluminum-silicon. The alloy contained about 98.35percent, by weight, aluminum and about 1.65 percent, by weight, silicon.Individual composites were prepared using 0.5, 1.0 and 2.0 percent, byweight, of the total metal additions of the agent lithiumfluoride-lithium chloride at temperatures of about 900, 1000, 1100 and1150 centigrade using the aforementoned procedure.

Example 14 A composite of about 50 percent, by weight, beryllium, about44.15 percent, by weight, aluminum, and the remainder silicon.

The procedure of Example 2 was followed using 50 percent, by weight,beryllium powder, mixed with about 50 percent, by weight, of an alloypowder of aluminumslicon. The alloy contained about 88.3 percent, byweight, aluminum and about 11.7 percent, by weight, silicon. Individualcomposites were prepared using 0.5, 1.0 and 2.0 percent, by weight, ofthe total metal additions of the agent lthium fluoride-lithium chlorideat temperatures of about 900, 1000, 1100 and 1150 centigrade for /2 hourand for 1 hour using the aforementioned procedure.

Example 15 A composite of about 85 percent, by weight, beryllium, about13.25 percent, by weight, aluminum, and the remainder silicon.

The procedure of Example 2 was followed using about 85 percent, bywei-ght, beryllium powder, mixed with about 15 percent, by weight, of analloy powder of aluminum-silicon. The alloy contained about 88.3percent, by Weight, aluminum and about 11.7 percent, by weight, silicon.Individual composites were prepared using 0.5, 1.0 and 2.0 percent, byweight, of the total metal additions of the agent lithiumfluoride-lithiurn chloride at temperatures of about 900, 1000, 1100 and1150 centigrade for /2 hour and for 1 hour using the aforementionedprocedure.

The present invention is not intended to be limited to the disclosureherein, and changes and modifications may be made in the disclosure bythose skilled in the art without departing from the spirit and scope ofthe novel concepts of this invention. Such modificatons and variationsare considered to be Within the purview and scope of this invention andthe appended claims.

Having thus described our invention, we claim:

1. A ternary metal composite consisting essentially of about -85percent, by weight, of beryllium, and the remainder an alloy ofaluminum-silicon.

2. A ternary metal composite according to claim 1, Wherein saidberyllium particles are surrounded by a matrix of an alloy ofaluminum-silicon-beryllium.

3. A metal composite according to claim 1, wherein said alloy containsabout 13.05 to 50.0 percent, by Weight, aluminum and a trace to about6.6 percent, by weight, silicon.

4. A ternary metal composite according to claim 1, wherein said matrixalloy contains about 87 to about 100.0 percent, by weight, aluminum andthe remainder silicon.

References Cited UNIT ED STATES PATENTS 2/1937 Donahue -150 4/1968Larsen 29-182.1

U.S. Cl. X.R. 29-182; 75-150

